System and method for actuating an engine valve

ABSTRACT

An engine valve actuator is provided. The actuator includes an actuator housing that defines a tank adapted to store a supply of fluid and a bore in fluid communication with the tank. A piston is slidably disposed in the bore of the actuator housing. The piston is adapted to move between a first position and a second position where the piston selectively engages an engine valve. A mechanical biasing element acts on the piston to move the piston towards the second position. A control valve is disposed between the tank and the bore in the actuator housing. The control valve is moveable between a first position where fluid is allowed to flow between the tank and the bore and a second position where fluid is prevented from flowing between the bore and the tank to trap fluid in the bore. The trapped fluid prevents the piston from moving with respect to the actuator housing to thereby prevent the engine valve from moving to a closed position.

TECHNICAL FIELD

The present invention is directed to a system and method for actuatingan engine valve and, more particularly, to an actuator for an enginevalve actuation system.

BACKGROUND

The operation of an internal combustion engine, such as, for example, adiesel, gasoline, or natural gas engine, may cause the generation ofundesirable emissions. These emissions, which may include particulatesand oxides of nitrogen (NOx), are generated when fuel is combusted in acombustion chamber of the engine. An exhaust stroke of an engine pistonforces exhaust gas, which may include these emissions, from the engine.If no emission reduction measures are in place, these undesirableemissions will eventually be exhausted to the environment.

Research is currently being directed towards decreasing the amount ofundesirable emissions that are exhausted to the environment during theoperation of an engine. It is expected that improved engine design andimproved control over engine operation may lead to a reduction in thegeneration of undesirable emissions. Many different approaches, such as,for example, engine gas recirculation and aftertreatments, have beenfound to reduce the amount of emissions generated during the operationof an engine. Unfortunately, the implementation of these emissionreduction approaches typically results in a decrease in the overallefficiency of the engine.

Additional efforts are being focused on improving engine efficiency tocompensate for the efficiency loss due to the emission reductionsystems. One such approach to improving the engine efficiency involvesadjusting the actuation timing of the engine valves. For example, theactuation timing of the intake and exhaust valves may be modified toimplement a variation on the typical diesel or Otto cycle known as theMiller cycle. In a “late intake” type Miller cycle, the intake valves ofthe engine are held open during a portion of the compression stroke ofthe piston. Implementing a timing variation, such as the late-intakeMiller cycle, may improve the overall efficiency of the engine.

The engine valves in an internal combustion engine are typically drivenby a cam arrangement that is operatively connected to the crankshaft ofthe engine. The rotation of the crankshaft results in a correspondingrotation of a cam that drives one or more cam followers. The movement ofthe cam followers results in the actuation of the engine valves. Theshape of the cam governs the timing and duration of the valve actuation.

An engine valve actuation system may include a hydraulic actuator thatis adapted to vary the valve actuation timing established by the shapeof the cam. For example, as described in U.S. Pat. No. 6,237,551 toMacor et al., issued on May 29, 2001, an engine valve actuation systemmay include a hydraulic actuator that establishes a hydraulic linkbetween the cam and the intake valve. When the link is established, thevalve will be actuated according to the shape of the cam. However, whenthe hydraulic link is broken, such as by opening a control valve, theforce of a valve return spring causes the engine valve to close. Thus,breaking the hydraulic link allows the engine valve to close at adifferent timing than would be achieved by the shape of the cam.

These types of hydraulic actuators typically use engine lubricating oilas the operating fluid. Lubricating oil may be supplied to the hydraulicactuator by a standard engine lubrication system. However, thelubricating oil may become contaminated with dirt, or debris, as thelubricating oil is circulated through the engine. Any such contaminationof the lubricating oil may lead to degraded performance of the hydraulicactuator, which may translate to a reduction in the overall efficiencyof the engine.

In addition, the operation of the hydraulic actuator may depend upon theviscosity of the lubricating oil. When the lubricating oil is cold, suchas when the engine is starting, the hydraulic actuator may experienceslow response times. Depending upon the current environmentalconditions, the engine may need to operate for a period of time to warmthe lubricating oil so that the hydraulic actuator will operate asexpected. The engine may experience rough running conditions ordifficulty starting until the lubricating oil is warmed enough to allowthe hydraulic actuator to operate properly.

The engine valve actuation system of the present invention solves one ormore of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to an engine valveactuator. The actuator includes an actuator housing that defines a tankadapted to store a supply of fluid and a bore in fluid communicationwith the tank. A piston is slidably disposed in the bore of the actuatorhousing. The piston is adapted to move between a first position and asecond position where the piston selectively engages an engine valve. Amechanical biasing element acts on the piston to move the piston towardsthe second position. A control valve is disposed between the tank andthe bore in the actuator housing. The control valve is moveable betweena first position where fluid is allowed to flow between the tank and thebore and a second position where fluid is prevented from flowing betweenthe bore and the tank to trap fluid in the bore. The trapped fluidprevents the piston from moving with respect to the actuator housing tothereby prevent the engine valve from moving to a closed position.

In another aspect, the present invention is directed to a method ofactuating an engine valve. A cam assembly is operated to move an enginevalve between a first position where the engine valve prevents a flow offluid and a second position where the engine valve allows a flow offluid. A piston is extended from an actuator housing to operativelyengage the engine valve. A flow of fluid is directed from a tank in theactuator housing to a bore in the actuator housing. The bore isassociated with the piston. Fluid is prevented from flowing from thebore to the tank to trap fluid in the bore and prevent the piston frommoving with respect to the actuator housing. The piston engages theengine valve to prevent the engine valve from returning to the firstposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic cross-sectional view of an exemplary embodimentof an internal combustion engine;

FIG. 2 is a diagrammatic cross-sectional view of a cylinder and valveactuation assembly in accordance with an exemplary embodiment of thepresent invention;

FIG. 3 is a schematic and diagrammatic cross-sectional representation ofan actuator for an engine valve in accordance with an exemplaryembodiment of the present invention;

FIG. 4 is a schematic and diagrammatic cross-sectional representation ofan actuator for an engine valve in accordance with an exemplaryembodiment of the present invention;

FIG. 5 is a schematic and diagrammatic cross-sectional representation ofan actuator for an engine valve in accordance with an exemplaryembodiment of the present invention; and

FIG. 6 is a graphic illustration of an exemplary valve actuation as afunction of engine crank angle for an engine operating in accordancewith the present invention.

DETAILED DESCRIPTION

An exemplary embodiment of an internal combustion engine 20 isillustrated in FIG. 1. For the purposes of the present disclosure,engine 20 is depicted and described as a four stroke diesel engine. Oneskilled in the art will recognize, however, that engine 20 may be anyother type of internal combustion engine, such as, for example, agasoline or natural gas engine.

As illustrated in FIG. 1, engine 20 includes an engine block 28 thatdefines a plurality of cylinders 22. A piston 24 is slidably disposedwithin each cylinder 22. In the illustrated embodiment, engine 20includes six cylinders 22 and six associated pistons 24. One skilled inthe art will readily recognize that engine 20 may include a greater orlesser number of pistons 24 and that pistons 24 may be disposed in an“in-line” configuration, a “V” configuration, or any other conventionalconfiguration.

As also shown in FIG. 1, engine 20 includes a crankshaft 27 that isrotatably disposed within engine block 28. A connecting rod 26 connectseach piston 24 to crankshaft 27. Each piston 24 is coupled to crankshaft27 so that a sliding motion of piston 24 within the respective cylinder22 results in a rotation of crankshaft 27. Similarly, a rotation ofcrankshaft 27 will result in a sliding motion of piston 24.

Engine 20 also includes a cylinder head 30. Cylinder head 30 defines anintake passageway 41 that leads to at least one intake port 36 for eachcylinder 22. Cylinder head 30 may further define two or more intakeports 36 for each cylinder 22.

An intake valve 32 is disposed within each intake port 36. Intake valve32 includes a valve element 40 that is configured to selectively blockintake port 36. As described in greater detail below, each intake valve32 may be actuated to move or “lift” valve element 40 to thereby openthe respective intake port 36. In a cylinder 22 having a pair of intakeports 36 and a pair of intake valves 32, the pair of intake valves 32may be actuated by a single valve actuation assembly or by a pair ofvalve actuation assemblies.

Cylinder head 30 also defines at least one exhaust port 38 for eachcylinder 22. Each exhaust port 38 leads from the respective cylinder 22to an exhaust passageway 43. Cylinder head 30 may further define two ormore exhaust ports 38 for each cylinder 22.

An exhaust valve 34 is disposed within each exhaust port 38. Exhaustvalve 34 includes a valve element 48 that is configured to selectivelyblock exhaust port 38. As described in greater detail below, eachexhaust valve 34 may be actuated to move or “lift” valve element 48 tothereby open the respective exhaust port 38. In a cylinder 22 having apair of exhaust ports 38 and a pair of exhaust valves 34, the pair ofexhaust valves 34 may be actuated by a single valve actuation assembly44 or by a pair of valve actuation assemblies 44.

FIG. 2 illustrates an exemplary embodiment of one cylinder 22 of engine20. As shown, cylinder head 30 defines a pair of intake ports 36connecting intake passageway 41 to cylinder 22. Each intake port 36includes a valve seat 50. One intake valve 32 is disposed within eachintake port 36. Valve element 40 of intake valve 32 is configured toengage valve seat 50. When intake valve 32 is in a closed position,valve element 40 engages valve seat 50 to close intake port 36 and blockfluid flow relative to cylinder 22. When intake valve 32 is lifted fromthe closed position, intake valve 32 allows a flow of fluid relative tocylinder 22.

Similarly, cylinder head 30 may define two or more exhaust ports 38(only one of which is illustrated in FIG. 1) that connect cylinder 22with exhaust passageway 43. One exhaust valve 34 is disposed within eachexhaust port 38. A valve element 48 of each exhaust valve 34 isconfigured to close exhaust port 38 when exhaust valve 34 is in a closedposition and block fluid flow relative to cylinder 22. When exhaustvalve 34 is lifted from the closed position, exhaust valve 32 allows aflow of fluid relative to cylinder 22.

As also shown in FIG. 2, a valve actuation assembly 44 is operativelyassociated with intake valves 32. Valve actuation assembly 44 includes abridge 54 that is connected to each valve element 40 through a pair ofvalve stems 46. A spring 56 may be disposed around each valve stem 46between cylinder head 30 and bridge 54. Spring 56 acts to bias bothvalve elements 40 into engagement with the respective valve seat 50 tothereby close each intake port 36.

Valve actuation assembly 44 also includes a rocker arm 64. Rocker arm 64is configured to pivot about a pivot 66. One end 68 of rocker arm 64 isconnected to bridge 54. The opposite end of rocker arm 64 is connectedto a cam assembly 52. In the exemplary embodiment of FIG. 2, the camassembly 52 includes a cam 60 having a cam lobe 63 and mounted on a camshaft 65, a push rod 61, and a cam follower 62. One skilled in the artwill recognize that cam assembly 52 may have other configurations, suchas, for example, where cam 60 acts directly on rocker arm 64.

Valve actuation assembly 44 may be driven by cam 60. Cam 60 is connectedto crankshaft 27 so that a rotation of crankshaft 27 induces acorresponding rotation of cam 60. Cam 60 may be connected to crankshaft27 through any means readily apparent to one skilled in the art, suchas, for example, through a gear train assembly (not shown). As oneskilled in the art will recognize, a rotation of cam 60 will cause camfollower 62 and associated push rod 61 to periodically reciprocatebetween an upper and a lower position.

The reciprocating movement of push rod 61 causes rocker arm 64 to pivotabout pivot 66. When push rod 61 moves in the direction indicated byarrow 58, rocker arm 64 will pivot and move bridge 54 in the oppositedirection. The movement of bridge 54 causes each intake valve 32 to liftand open intake ports 36. As cam 60 continues to rotate, springs 56 willact on bridge 54 to return each intake valve 32 to the closed position.

In this manner, the shape and orientation of cam 60 controls the timingof the actuation of intake valves 32. As one skilled in the art willrecognize, cam 60 may be configured to coordinate the actuation ofintake valves 32 with the movement of piston 24. For example, intakevalves 32 may be actuated to open intake ports 36 when piston 24 ismoving from a top-dead-center position towards a bottom-dead-centerposition in an intake stroke to allow air to flow from intake passageway41 into cylinder 22.

A similar valve actuation assembly may be connected to exhaust valves34. A second cam (not shown) may be connected to crankshaft 27 tocontrol the actuation timing of exhaust valves 34. Exhaust valves 34 maybe actuated to open exhaust ports 38 when piston 24 is moving from abottom-dead-center position towards a top-dead-center position to allowexhaust to flow from cylinder 22 into exhaust passageway 43.

As shown in FIG. 2, valve actuation assembly 44 may also include anactuator 70. Actuator 70 includes a housing 72 that slidably receives apiston 74 having an end 75. End 75 of piston 74 is adapted to engage end68 of rocker arm 64. One skilled in the art will recognize that end 75of piston may engage another portion of rocker arm or may be operativelyengaged with valve actuation assembly 44 in another way.

As schematically shown in FIG. 3, housing 72 of actuator 70 defines atank 78. Tank 78 is adapted to store a supply of fluid. Tank 78 maystore any type of fluid such as, for example, an engine lubricating oil.

Housing 72 of actuator 70 also defines a bore 80 that is adapted toslidably receive piston 74. A seal 73 may be disposed between piston 74and bore 80. Seal 73 may be any type of sealing element adapted toprevent fluid from escaping from bore 80 past piston 74.

A mechanical biasing means may be disposed in bore 80. The mechanicalbiasing means acts on piston 74 to bias piston 74 away from housing 72,i.e. in the direction of arrow 77. The mechanical biasing means may beany mechanical biasing element, such as, for example, a spring 76, thatis adapted to bias piston 74 away from housing 72. The force exerted bythe mechanical biasing means may be less than the force exerted bysprings 56 (referring to FIG. 2) on bridge 54.

Housing 72 of actuator 70 also defines a fluid passageway 86 thatconnects tank 78 and bore 80. Fluid passageway 86 provides a fluidconnection that allows fluid to flow between the tank 78 and the bore80. For example, fluid may flow from tank 78 to bore 80 as spring 76biases piston 74 away from housing 72.

A control valve 82 may be disposed in fluid passageway 86. Control valve82 may be moved between a first position where fluid is allowed to flowthrough fluid passageway 86 and a second position, where fluid isprevented from flowing through fluid passageway 86. Thus, by controllingthe position of control valve 82, the rate of fluid flow between thetank 78 and the bore 80 may be controlled.

A snubbing valve 93 may be disposed in the fluid line between bore 80and control valve 82. Snubbing valve 93 may be configured to decreasethe rate at which fluid exits bore 80 to thereby slow the rate at whichpiston 74 moves within bore 80. Snubbing valve 93 may include one ormore passageways 95 having openings that connect bore 80 with the fluidline leading to control valve 82.

A bleed valve 94 may be disposed in housing 72. Bleed valve 94 may beadapted to allow air, or any other gas, that finds it way into tank 78to be released from tank 78. This will prevent air from being passedfrom tank 78 to bore 80. Bleed valve 94 may also purge air from anywherein actuator 70.

Actuator 70 may also include an accumulator 84. As shown in FIGS. 3–5,accumulator 84 may include a piston 87 disposed in a chamber 89. Aspring 85 may act on piston 87. Fluid entering chamber 89 may act tomove piston 87 and compress spring 85 if the force exerted by the fluidon piston 87 is great enough to overcome the force of spring 85. Spring85 may act to move piston 87 and force fluid out of chamber 89 when theforce of spring 85 is greater than the force exerted by the pressurizedfluid on piston 87.

A fluid passageway 88 may connect accumulator 84 to fluid passageway 86between the tank 78 and the bore 80. A restrictive orifice 91 may bedisposed in an inlet to accumulator 84. As described in greater detailbelow, accumulator 84 may act to dampen oscillations in bore 80 andfluid passageway 86, which may cause piston 74 to oscillate relative tohousing 72.

Housing 72 of actuator 70 also includes one or more leak passageways 90and 92. Leak passageways 90 and 92 may be adapted to allow fluid thatleaks from either control valve 82 or accumulator 84 to return to tank78. As described in greater detail below, both control valve 82 andaccumulator 84 may be exposed to fluid having a substantial pressure.Leak passageway 90 and 92 may help prevent any fluid that leaks throughcontrol valve 82 or accumulator 84 from leaking from actuator 70.

As illustrated in FIG. 4, a spring loaded piston 96 may be disposed intank 78. Spring loaded piston 96 may act to exert a force on fluidcontained in tank 78. The force of piston 96 may act to increase thepressure of the fluid in tank 78 and to thereby move fluid through fluidpassageway 86 to bore 80.

As shown in FIG. 5, housing 72 of actuator 70 may include a thirdchamber 97 disposed between tank 78 and control valve 82. Chamber 97 mayinclude spring loaded piston 96. A check valve 98 may be disposed inpiston 96. Check valve 98 may be configured to allow fluid to flow fromtank 78 towards bore 80. In this manner, check valve 98 is adapted toallow for the replacement of fluid that may leak from actuator 70.

As shown in FIG. 2, housing 72 of actuator 70 may be connected tocylinder head 30. For example, a pair of supports 81 may extend fromhousing 72 to cylinder head 30. Supports 81 may be attached to cylinderhead 30 by any connecting member readily apparent to one skilled theart. For example, bolts 83 may connect supports 81 to cylinder head 30.

As shown in FIG. 1, a controller 100 is connected to control valve 82 ineach valve actuation assembly 44. Controller 100 may include anelectronic control module that has a microprocessor and a memory. As isknown to those skilled in the art, the memory is connected to themicroprocessor and stores an instruction set and variables. Associatedwith the microprocessor and part of electronic control module arevarious other known circuits such as, for example, power supplycircuitry, signal conditioning circuitry, and solenoid driver circuitry,among others.

Controller 100 may be programmed to control one or more aspects of theoperation of engine 20. For example, controller 100 may be programmed tocontrol the valve actuation assembly, the fuel injection system, and anyother function readily apparent to one skilled in the art. Controller100 may control engine 20 based on the current operating conditions ofthe engine and/or instructions received from an operator. As shown inFIGS. 3–5, controller 100 is connected to control valve 82 in actuatorhousing 72 through a lead 101.

Controller 100 may be further programmed to receive information from oneor more sensors operatively connected with engine 20. Each of thesensors may be configured to sense one or more operational parameters ofengine 20. One skilled in the art will recognize that many types ofsensors may be used in conjunction with engine 20. For example, engine20 may be equipped with sensors configured to sense one or more of thefollowing: the temperature of the engine coolant, the temperature of theengine, the ambient air temperature, the engine speed, the load on theengine, the intake air pressure, the position of the piston relative tothe cylinder, and the pressure in the cylinder.

Engine 20 may be further equipped with a sensor configured to monitorthe crank angle of crankshaft 27 to thereby determine the position ofpistons 24 within their respective cylinders 22. The crank angle ofcrankshaft 27 is also related to actuation timing of intake valves 32and exhaust valves 34. An exemplary graph 102 indicating therelationship between valve actuation timing and crank angle isillustrated in FIG. 6. As shown by graph 102, the exhaust valve lift 104is timed to substantially coincide with the exhaust stroke of piston 24and the intake valve lift 106 is timed to substantially coincide withthe intake stroke of piston 24.

INDUSTRIAL APPLICABILITY

Based on information provided by the engine sensors, controller 100 mayoperate control valve 82 in each valve actuation assembly 44 to controlthe actuation timing of the valves of engine 20. For example, undercertain operating conditions, controller 100 may implement a late intakeMiller cycle in each cylinder 22 of engine 20. Under normal operatingconditions, implementation of the late intake Miller cycle may increasethe overall efficiency of the engine 20. However, under some operatingconditions, such as, for example, when engine 20 is cold, controller 100may operate engine 20 on a conventional diesel cycle.

The following discussion describes the implementation of a late intakeMiller cycle in a single cylinder 22 of engine 20. One skilled in theart will recognize that the system of the present invention may be usedto selectively implement a late intake Miller cycle in all cylinders ofengine 20 in the same or a similar manner. In addition, the system ofthe present invention may be used to implement other valve actuationvariations on the conventional diesel cycle, such as, for example,exhaust gas re-circulation system.

Controller 100 may implement a late intake valve closing Miller cyclefor a particular cylinder 22 by controlling the position of controlvalve 82 in valve actuation assembly 44. The rotation of cam 60 causesrocker arm 64 to pivot to thereby actuate intake valves 32. The force ofspring 76 causes piston 74 to extend in the direction of arrow 77(referring to FIG. 3), to thereby follow the motion of end 68 of rockerarm 64.

The movement of piston 74 in bore 80 draws fluid into bore 80 from fluidpassageway 86 and tank 78. The flow of fluid into bore 80 may be aidedby spring-loaded piston 96, which may be disposed in tank 78 (as shownin FIG. 4) or in chamber 97 (as shown in FIG. 5). Spring-loaded piston96 may act to force fluid through fluid passageway 86 into bore 80 toensure that bore 80 is filled with fluid.

Controller 100 may send a signal to adjust the position of control valve82 to close passageway 86 and thereby trap fluid in bore 80 when piston74 is fully extended from housing 72. For example, controller 100 mayclose control valve 82 when intake valve 32 is at or near a maximum liftposition, such as, for example, a peak 107 (referring to FIG. 6)distance. Also, controller 100 may time the closing of control valve 82to ensure that bore 80 is filled with fluid before control valve 82 ismoved to the closed position.

As cam 60 continues to rotate, springs 56 urge intake valves 32 towardstheir closed position until end 68 of rocker arm 64 engages end 75 ofpiston 74. The fluid trapped in bore 80 will prevent piston 74 frommoving with respect to housing 72 and will, therefore, prevent intakevalves 32 from closing. As long as control valve 82 remains in theclosed position, the trapped fluid in bore 80 will prevent springs 56from returning intake valves 32 to the closed position. Thus, actuator70 will hold intake valves 32 in the open position, independently of theaction of cam assembly 52.

When rocker arm 64 engages piston 74, the force of springs 56 actingthrough rocker arm 64 may cause an increase in the pressure of the fluidwithin actuator 70. In response to the increased pressure, fluid willflow through restrictive orifice 91 in passageway 88 and intoaccumulator 84, which may absorb the pressure spike. In this manner,accumulator 84 may act to dampen any oscillations that may result fromthe engagement of rocker arm 64 and piston 74.

Controller 100 may close intake valves 32 by sending a signal to adjustthe position of control valve 82 to open passageway 86. This allows thetrapped fluid to flow out of bore 80. The force of springs 56 overcomesthe force of spring 76 and forces the fluid from bore 80 towards tank78. The release of the trapped fluid allows piston 74 to move withinhousing 72. This allows rocker arm 64 to pivot so that intake valves 32are moved to the closed position.

Snubbing valve 93 may reduce the rate at which intake valve 32 moves tothe closed position. As piston 74 moves within bore 80, fluid flowsthrough passageways 95. The body of piston 74 will eventually block theopenings to passageways 95, thereby reducing the rate at which fluidflows from bore 80. This reduction in fluid flow rate translates to areduction in velocity of piston 74 and to a reduction in the closing, orseating, velocity of intake valves 32. In this manner, snubbing valve 93controls the velocity at which intake valves 32 close to prevent theintake valves 32 from being damaged.

An exemplary late intake closing 108 is illustrated in FIG. 6. As shown,the intake valve actuation 106 is extended into a portion of thecompression stroke of piston 24. This allows some of the air in cylinder22 to escape as piston 24 begins the compression stroke. The amount ofair allowed to escape cylinder 22 may be controlled by adjusting thecrank angle at which control valve 82 is opened. Control valve 82 may beopened at an earlier crank angle to decrease the amount of escaping airor at a later crank angle to increase the amount of escaping air.

Certain operating conditions may require that engine 20 be operated on aconventional diesel cycle instead of the late intake Miller cycledescribed above. These types of operating conditions may be experienced,for example, when engine 20 is first starting or is otherwise operatingunder cold conditions. The described valve actuation system 44 allowsfor the selective disengagement of the late intake Miller cycle.

Controller 100 may disengage the late intake Miller cycle by leavingcontrol valve 82 in the open position. If control valve 82 iscontinuously open, no fluid will be trapped in bore 80. Accordingly,piston 74 will be free to move within housing 72 and will not preventintake valves 32 from returning to the closed position. Thus, theactuation of intake valves 32 will be driven by the shape of cam 60.

Thus, when control valve 82 is continuously open, intake valves 32 willfollow a conventional diesel cycle as governed by cam 60. As shown inFIG. 6, intake valve actuation 106 will follow a conventional closing110. In the conventional closing 110, the closing of intake valves 32substantially coincides with the end of the intake stroke of piston 24.When intake valves 32 close at the end of the intake stroke, no air willbe forced from cylinder 22 during the compression stroke. This resultsin piston 24 compressing the fuel and air mixture to a higher pressure,which will facilitate diesel fuel combustion. This is particularlybeneficial when engine 20 is operating in cold conditions.

As will be apparent from the foregoing description, the described systemprovides an engine valve actuation system that may selectively alter thetiming of the intake and/or exhaust valve actuation of an internalcombustion engine. The actuation of the engine valves may be based onsensed operating conditions of the engine. For example, the engine valveactuation system may implement a late intake Miller cycle when theengine is operating under normal operating conditions. The late intakeMiller cycle may be disengaged when the engine is operating underadverse operating conditions, such as when the engine is cold. Thus, thedisclosed system and method provide a flexible engine valve actuationsystem that provides for both enhanced cold starting capability and fuelefficiency gains.

The disclosed system and method also provides an engine valve actuatorthat is self-contained in a single housing. All essential elements ofthe actuator are contained in the housing, including the fluid supplyreservoir. As the actuator does not have to share fluid with anothersystem in the engine, the possibility of operating fluid contaminationis reduced. Also, the actuator may use any type of operating fluid,including a fluid that is not affected by a change in temperature. Thus,the disclosed actuator may not experience performance problems when theoperating fluid is cold.

In addition, the described hydraulic actuator does not rely upon oilfrom the engine lubrication system. Accordingly, any contamination ofthe lubricating oil will not affect the operation of the hydraulicactuator. Also, as the amount of fluid stored in the actuator issubstantially less than the amount of oil included in the enginelubrication system, the fluid in the described actuator may reach anormal operating temperature faster than the oil in the enginelubricating system. Thus, the described actuator may provide forreliable and timely operation, even under undesirable operatingconditions.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the described engine valveactuation system without departing from the scope of the invention.Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope of theinvention being indicated by the following claims and their equivalents.

1. An engine valve actuator, comprising: an actuator housing defining atank adapted to store a supply of fluid and a bore in fluidcommunication with the tank; a piston slidably disposed in the bore ofthe actuator housing, the piston adapted to move between a firstposition and a second position where the piston engages an engine valve;a mechanical biasing element acting on the piston to move the pistontowards the second position; and a control valve disposed between thetank and the bore in the actuator housing, the control valve selectivelymoveable between a first position where fluid is allowed to flow betweenthe tank and the bore and a second position where fluid is preventedfrom flowing between the bore and the tank to trap fluid in the bore,the trapped fluid preventing the piston from moving with respect to theactuator housing to thereby prevent the engine valve from returning to aclosed position.
 2. The actuator of claim 1, wherein the mechanicalbiasing element is a spring.
 3. The actuator of claim 1, furtherincluding: an accumulator disposed in the actuator housing and in fluidconnection with the tank and the bore; and a restrictive orificedisposed at the inlet to the accumulator.
 4. The actuator of claim 3,further including a first leak passageway connecting the accumulatorwith the tank.
 5. The actuator of claim 4, further including a secondleak passageway connecting the control valve with the tank.
 6. Theactuator of claim 1, further including an air-bleed valve adapted toallow air to escape from the tank.
 7. The actuator of claim 1, whereinthe tank includes a spring-loaded piston.
 8. The actuator of claim 1,wherein the actuator housing defines a chamber between the tank and thebore and wherein the chamber includes a spring-loaded piston.
 9. Theactuator of claim 8, further including a check valve disposed in thechamber and adapted to allow fluid to flow from the tank towards thebore.
 10. The actuator of claim 1, further including a snubbing valveadapted to slow a seating velocity of the piston.
 11. The engine valveactuator of claim 1, wherein preventing the engine valve from returningto a closed position extends an engine valve lift period.
 12. The enginevalve actuator of claim 1, wherein preventing the engine valve fromreturning to a closed position increases an average valve lift heightduring a valve lift period.
 13. An engine valve actuator, comprising: anactuator housing defining a tank adapted to store a supply of fluid anda bore in fluid communication with the tank; a piston slidably disposedin the bore of the actuator housing and moveable between a firstposition and a second position where the piston engages an engine valve;a mechanical biasing means for moving the piston relative towards thesecond position; and a flow control means for controlling a flow offluid between the tank and the bore, the flow control means adapted toselectively prevent the flow of fluid between the tank and the bore totrap fluid in the bore, the trapped fluid preventing the piston frommoving with respect to the actuator housing to thereby prevent theengine valve from returning to a closed position.
 14. The actuator ofclaim 13, wherein the mechanical biasing means is a spring disposedbetween the piston and the actuator housing, the spring adapted to biasthe piston into operative engagement with the engine valve.
 15. Theactuator of claim 13, further including a means for dampening pressurefluctuations in a fluid passageway connecting the tank and the bore. 16.The actuator of claim 13, wherein the flow control means is a controlvalve moveable between a first position where fluid is allowed to flowbetween the tank and the bore and a second position where fluid isprevented from flowing between the bore and the tank.
 17. The enginevalve actuator of claim 13, wherein preventing the engine valve fromreturning to a closed position extends an engine valve lift period. 18.The engine valve actuator of claim 13, wherein preventing the enginevalve from returning to a closed position increases an average valvelift height during a valve lift period.
 19. A method of actuating anengine valve, comprising: operating a cam assembly to move an enginevalve between a first position where the engine valve prevents a flow offluid and a second position where the engine valve allows a flow offluid; extending a piston from an actuator housing to engage the enginevalve; directing a flow of fluid from a tank disposed within theactuator housing to a bore in the actuator housing, the bore beingassociated with the piston; and selectively preventing fluid fromflowing from the bore to the tank to trap fluid in the bore and preventthe piston from moving with respect to the actuator housing, the pistonengaging the engine valve to prevent the engine valve from returning tothe first position.
 20. The method of claim 19, further includingallowing fluid to flow from the bore to the tank to release the pistonand thereby allow the engine valve to return to the first position. 21.The method of claim 20, wherein fluid is allowed to flow from the boreto the tank after a predetermined period of time.
 22. The method ofclaim 19, further including directing a portion of the flow of fluidbetween the tank and the bore to an accumulator.
 23. The engine valveactuator of claim 19, wherein preventing the engine valve from returningto a closed position extends an engine valve lift period created by thecam assembly.
 24. The engine valve actuator of claim 19, whereinpreventing the engine valve from returning to a closed positionincreases an average valve lift height during a valve lift periodcreated by the cam assembly.
 25. An engine valve actuation system,comprising: an engine valve moveable between a first position where theengine valve prevents a flow of fluid and a second position where theengine valve allows a flow of fluid; a spring acting on the engine valveto move the engine valve towards the first position; a cam assemblyoperatively connected to the engine valve to move the engine valvebetween the first position and the second position; an actuator housingdefining a tank adapted to store a supply of fluid and a bore in fluidcommunication with the tank; a piston slidably disposed in the bore ofthe actuator housing, the piston adapted to engage the engine valve; amechanical biasing element acting on the piston to move the piston tooperatively engage the engine valve; and a control valve disposedbetween the tank and the bore in the actuator housing, the control valveselectively moveable between a first position where fluid is allowed toflow between the tank and the bore and a second position where fluid isprevented from flowing from the bore to the tank to trap fluid in thebore, the trapped fluid preventing the piston from moving with respectto the actuator housing to thereby prevent the engine valve fromreturning to the first position.
 26. The engine valve actuation systemof claim 25, wherein the mechanical biasing element is a spring.
 27. Theengine valve actuation system of claim 25, further including anaccumulator disposed in the actuator housing and in fluid connectionwith the tank and the bore.
 28. The engine valve actuation system ofclaim 25, further including an air-bleed valve adapted to allow air toescape from the tank.
 29. The engine valve actuation system of claim 25,wherein the tank includes a spring-loaded piston.
 30. The engine valveactuation system of claim 25, wherein the actuator housing defines achamber between the tank and the bore and wherein the chamber includes aspring loaded piston.
 31. The engine valve actuation system of claim 30,further including a check valve disposed in the chamber and adapted toallow fluid to flow from the tank towards the bore.
 32. The engine valveactuation system of claim 25, further including a pair of supportsadapted to secure the actuator housing to a cylinder head.
 33. Theengine valve actuator of claim 25, wherein preventing the engine valvefrom returning to a closed position extends an engine valve lift periodcreated by the cam assembly.
 34. The engine valve actuator of claim 25,wherein preventing the engine valve from returning to a closed positionincreases an average valve lift height during a valve lift periodcreated by the cam assembly.
 35. A self-contained engine valve actuationarrangement adapted to selectively engage an engine valve moveablerelative to a cylinder head: an actuator housing defining a tankcontaining a closed supply of fluid and a bore in fluid communicationwith the tank, the actuator being fixed to the cylinder head; a pistonslidably disposed in the bore of the actuator housing, the pistonadapted to move between a first position and a second position where thepiston engages an engine valve; a mechanical biasing element acting onthe piston to move the piston towards the second position; and a controlvalve disposed between the tank and the bore in the actuator housing,the control valve selectively moveable between a first position wherefluid is allowed to flow between the tank and the bore and a secondposition where fluid is prevented from flowing between the bore and thetank to trap fluid in the bore, the trapped fluid preventing the pistonfrom moving with respect to the actuator housing to thereby prevent theengine valve from returning to a closed position.
 36. The arrangement ofclaim 35, further including a support structure connecting the actuatorhousing to the cylinder head.
 37. The arrangement of claim 36, whereinthe support structure is bolted to the cylinder head.
 38. The enginevalve actuator of claim 35, wherein preventing the engine valve fromreturning to a closed position extends an engine valve lift period. 39.The engine valve actuator of claim 35, wherein preventing the enginevalve from returning to a closed position increases an average valvelift height during a valve lift period.